Up to now, turbine part refurbishing providers can only repair parts of an industrial gas turbine (IGT) with the goal to restore their original integrity, optionally including certain limited and local design changes in order to improve the turbine performance, overcome premature part degradation or even failures during standard operation regimes (base load, low to medium cyclic load).
A lot of prior art publications describe modular/hybrid IGT part concepts including repair approaches.
Document U.S. Pat. No. 7,670,116 B1 discloses a vane for use in a gas turbine engine, which vane is made of an exotic, high temperature material that is difficult to machine or cast. The vane includes a shell made from either Molybdenum, Niobium, alloys of Molybdenum or Niobium (Columbium), Oxide Ceramic Matrix Composite (CMC), or SiC—SiC ceramic matrix composite, and is formed from a wire electric discharge process. The shell is positioned in grooves between the outer and inner shrouds, and includes a central passageway within the spar, and forms a cooling fluid passageway between the spar and the shell. Both the spar and the shell include cooling holes to carry cooling fluid from the central passageway to an outer surface of the vane for cooling. This cooling path eliminates a serpentine pathway, and therefore requires less pressure and less amounts of cooling fluid to cool the vane.
Document U.S. Pat. No. 5,797,725 discloses a gas turbine engine vane and method of its manufacture. The vane is non-destructively removable from a vane segment to allow individual components to be replaced. The vane and end walls are coupled together by a retainer that is formed in place between the vane and the end wall and that can be removed by conventional techniques. In one form the retainer fills a pair of corresponding grooves in the vane and end wall member so as to mechanically couple the components together and minimize fluid leakage there between. The retainer is non-metallurgically coupled to the vane and end wall member. A portion of the vane is allowed to move relative to the end wall in response to thermal conditions.
Document U.S. Pat. No. 5,269,057 teaches a method for replacing airfoil components including the steps of identifying a portion of the airfoil to be replaced, removing the portion by a nonconventional machining process, such as continuous wire electrical discharge machining, and forming a replacement member utilizing a similar cutting process. A cutting path utilized to remove the portion to be replaced and to form the replacement member includes interlocking projections and sockets and may include one or more tapers along the cutting path so that the portion may be removed only by lifting in one direction. In cases where an entire airfoil is replaced, a first projection may be tapered in one direction while a second projection is tapered in an opposite direction so that the airfoil may not be removed as long as its adjacent flow path walls are fixed relative to one another. Gas bending load dampers and zero gap standoffs may also be included for precision alignment of the replacement member and further securement of the replacement member in the airfoil.
Document EP 2 196 624 A1 discloses a blade with a blade vane, a blade tip, a blade root and a platform that is formed between the blade tip and the blade root. A tie rod, a lower blade part and an upper blade part are made of different materials based on the application, where material properties are adaptable to respective local loads. The dimensions of the tie rod, the upper blade part and the lower blade part are clearly lesser than the dimension of the blade. The tie rod, the upper blade part and the lower blade part are connected together partly by a form closure.
Document EP 2 009 243 A2 discloses a turbine vane, which has an airfoil shell and a spar within the shell. The vane has an outboard shroud at an outboard end of the shell and an inboard platform at an inboard end of the shell. The shell includes a region having a depth-wise coefficient of thermal expansion and a second coefficient of thermal expansion transverse thereto, the depth-wise coefficient of thermal expansion being greater than the second coefficient of thermal expansion.
Document WO 2010/028913 A1 relates to a turbine blade for a gas turbine, wherein the trailing edge region designed in the manner of a cut-back trailing edge has a modular design. For this purpose, the region of the trailing edge of the blade is provided with a slot extending from the platform to the blade tip, wherein an insert component, in which the webs typical of a cut-back trailing edge are configured, is disposed in said slot. The insert thus comprises channels which are disposed between the webs and end in openings, from which coolant that can flow on the inside of the blade can flow out of the blade. With the proposed measure, a casting core that is further reinforced in the trailing edge region can be used for producing the cast blade, whereby the mechanical integrity thereof is improved and it has a lower tendency to break during the handling thereof. In addition, when using such a turbine blade the quantity of cooling air exiting at the trailing edge can be set comparatively accurately by way of a non-cast, conventionally produced insert.
Document U.S. Pat. No. 7,452,182 relates to a modular turbine vane assembly. The vane assembly includes an airfoil portion, an outer shroud and an inner shroud. The airfoil portion can be made of at least two segments. Preferably, the components are connected together so as to permit assembly and disassembly of the vane. Thus, in the event of damage to the vane, repair involves the replacement of only the damaged subcomponents as opposed to the entire vane. The modular design facilitates the use of various materials in the vane, including materials that are dissimilar. Thus, suitable materials can be selected to optimize component life, cooling air usage, aerodynamic performance, and cost. Because the vane is an assemblage of smaller sub-components as opposed to one unitary structure, the individual components of the vane can be more easily manufactured and more intricate features can be included.
Document EP 2 189 626 refers to a rotor blade arrangement, especially for a gas turbine, which rotor blade arrangement can be fastened on a blade carrier and comprises in each case a blade aerofoil element and a platform element, wherein the platform elements of a blade row form a continuous inner shroud. With such a blade arrangement, a mechanical decoupling, which extends the service life, is achieved by blade aerofoil element and platform element being formed as separate elements and by being able to be fastened in each case separately on the blade carrier.
Document WO 2013/017433 A1 relates to a method for creating a blade for a flow force engine and to such a blade. According to the invention, components are produced by an additive production method such as selective laser melting, while a main body is produced by casting, for example. The blade components can consist of a different material or carry functions such as serving as drainage slots, for example. The advantage is that the expense related to the use of additive production methods occurs only for the components in which a complicated geometry, for example, must be implemented. The remaining components in the form of the main body, comprising the blade, the blade foot and the blade head, can be cost-effectively implemented as a cast part or a sheet metal part.
The well known, widely established, standard (best practice) reconditioning procedures of IGT hot gas path parts have the following disadvantages:                Repaired parts get a standard reconditioning only, in order to fulfill the original new make (OH/cycle/EOH) target conditions for a second, third or an extended subsequent operation interval;        no considerable design changes can be adopted without affecting or risking the parts, i.e. their mechanical integrity;        no considerable design changes can be adopted without implying significant (time consuming and high cost) efforts;        only local and limited design improvements do not allow significant changes in operation regime (a transition from base load operation to cyclic load/“peaker” operation is impossible);        parts with consumed cyclic lifetime (from previous accomplished operation intervals) cannot be restored anymore to allow another subsequent cyclic or even high cyclic (“peaker”) operation regime. It is expected that the future power market will rather ask for cyclic lifetime than for operation hours, generally leading to an earlier expiry of cycles than operation time;        parts with (locally) material based limitations (oxidation/corrosion and/or mechanical/physical properties) cannot be improved without exchanging the material at least in areas with restricted lifetime limits resulting from original design;        parts with (locally) coating system and/or material based limitations (oxidation/corrosion and/or mechanical/physical properties) cannot be improved without exchanging the material and/or coating system at least at the areas with restricted lifetime limits;        parts with locally coating system and/or material and/or design based limitations (creep, low cycle fatigue LCF) cannot be improved without exchanging the material and/or coating system and/or by significantly changing the design at least at the areas with restricted lifetime limits.        
Without complementing known and established standard refurbishment approaches, customers (a) cannot or (b) cannot reliably or (c) can only by shortening operation intervals and frequently replacing turbine parts, operate their industrial gas turbines (IGTs) within future electric grids ruled by continuously increasing demand for even higher operational flexibility (significantly higher cycling and/or part load operation).
The latter aspect is due to (a) a steadily growing amount of renewable energy sources in electric power grids, (b) changing gas prices and (c) local market energy overcapacities. In the future, gas turbine combined-cycle (GTCC) power plants can only keep or expand its share in power production, if customers will be able to reliably run their plants with favorable cost/KWh as secondary and tertiary response units.